The present invention relates to a longitudinally extending sling which provides support and comfort for the medial arch of the foot. More particularly, the present invention relates to a sling which is anchored in the outsole of a shoe so as to control the girthing forces on the foot by maintaining the effective length of the longitudinal portion of the shoe. The present invention achieves some of the same benefits which have been previously obtained by taping of the foot as in the "Low Dye Strap" described hereinafter. However, the longitudinal constraint is obtained by anchoring in the shoe rather than by the use of tape on the foot itself.
In an attempt to understand the foot as a system, the various parameters which affect the function of the foot have been studied, particularly with regard to a weight bearing foot. The practical need for such knowledge lies in the fact that a true structural model of the foot is capable of providing a prediction of gait and the effects of a shoe on gait. By knowing, in advance, how a shoe would affect the performance of an athlete, for example, optimum shoes could be designed without the usual "cut and try" method of standard shoe development.
The traditional model of the foot provides for a one column, two-axis model which maintains that the foot under load is a rigid structure with a talocrural (ankle) axis and an apparent subtalar axis. The front of the foot is relatively rigid, but with only a multitude of small bone movements about the midtarses axes. The average direction of the effective axis under the ankle, called the subtalar axis, is said to be 42 degrees vertical and 16 degrees horizontal to the midline of the body, as measured by Inman, V. T., The Joints of the Ankle, The Williams & Wilkins Co., Baltimore, 1976. However, this theory does not hold up with regard to a weight bearing or loaded foot since, if the force due to body weight were to act on the single traditional subtalar axis, the foot would collapse mechanically.
It has now been determined that the foot is comprised of two columns and three axes. The lower, lateral column is basically a rigid base comprised of the Calcaneus, Cuboid, and the fourth and fifth metatarsals. The remainder of the foot, which is comprised of the navicular, the first, second and third cuneiforms and the first, second and third metatarsals, emanates from the talus at the talonavicular interface swinging in combination with the lower column inversion/eversion actions in what may be called the `subtalar joint axis`. But this articulation of what is called the upper foot column is only secondary to the true foot mechanism. The primary mechanical loading interface is on the lower, lateral column at the rear of the talus onto the calcaneus, the posterior talocalcaneal facet.
It has also been determined that the foot operates differently under load than when it is passively manipulated such as a doctor would do in the office. This distinction helps to explain previous misconceptions as to how the foot works under load.
This new understanding has yielded a new structural model of the foot which has two separate columns, wrapped together with fascia, and three nearly orthogonal axes. The three axes are: (1) the talocrural (ankle) axis; (2) the talocalcaneal axis (formed at the facet between the talus and the calcaneus); and (3) the talonavicular axis (formed at the facet between the talus and the navicular bones).
The longitudinal support sling of the present invention represents a novel structure which is based on providing a supplement to the longitudinal fascia, ligaments and tendons of the foot. This supplement could be either static or dynamic. The longitudinal sling of the present invention is, in some respects, related to the well-known "Low Dye Strap" taping procedure used by podiatrists to support and comfort the medial arch of the foot.
The concept of the longitudinal support sling of the present invention as it relates to the shoe is based on the fact that, due to the physical structure of the foot, as the heel is loaded, it expands and the foot lengthens. By constraining the length between the heel and the ball of the foot, the arch is supported. The present longitudinal sling is most effective when employed with and anchored to a relatively flexible outsole. On the medial side of the foot, the sling pulls from a point just forward of the first metatarsal head. On the lateral side, the sling pulls from a point adjacent the posterior portion of the fifth metatarsal. The sling could also be anchored to transverse shoe components in the midfoot region.
As the person wearing the sling loads the foot such as while walking, the straps apply a horizontal force which aids the arch. Upon stepping down, a definite tightening of the straps can be felt. In order for the full pressure to be felt, both the rearfoot and forefoot need to be in contact with the ground. Total forefoot freedom is available with the present sling and there is a very comfortable heel girth.
In one embodiment, the longitudinal support sling of the present invention includes a medial-lateral connector strap which extends across the top of the foot in the forefoot region and interconnects the medial and lateral sling portions proximate to the anterior portions thereof. The support sling may be anchored to the outsole in the region under the toes. A heel strap may be secured to the rear heel portion of the outsole, with the heel strap having a loop for receiving the posterior portion of the support sling.
In an embodiment in which the longitudinal support sling is sewn into the outsole of a shoe, the medial-lateral connector strap would not be necessary since the sling would be anchored to the outsole. In such an embodiment, the support sling would be adhered or sewn to the outsole and thus it would not be necessary for the sling to pass all the way across the outsole in the region under the toes. In addition, there would be no need for a heel strap or loop in such an embodiment.
In order to obtain a sufficiently tight girth, the support sling girth may be adjusted before the connector strap is put in place. Then, with no load on the foot, the connector strap is secured around the medial and lateral sling portions.
The advantages of the longitudinal support sling of the present invention over the prior art devices include the fact that a perceptible feeling of support and comfort is obtained, similar in some respects to that obtained with previous taping methods, but with the advantage that the present support sling forms an integral part of the shoe. In addition, the tensioning effect of the present sling is enhanced by allowing the strap to slide around the heel instead of being adhered to it. The present invention also creates a dynamic heel cupping mechanism unlike previous shoe constructions.
Accordingly, it is a primary object of the present invention to obtain a shoe construction which provides longitudinal support to the longitudinal fascia, ligaments and tendons of the foot.
It is a further object of the invention to provide advantageous heel cushion constraint.
It is an additional object of the present invention to interactively enhance gait dynamics by linking the rear and forefoot areas.
An additional object of the present invention is to enhance the customization of heel fit in a shoe construction.